The present invention relates to a method and an apparatus for manufacturing a constant velocity joint and more particularly an outer race thereof.
The constant velocity joint to be manufactured by the present invention is a joint for use in a front wheel drive vehicle, and it is a joint which transmits rotation from a drive axle to a driven one at the same speed so as to cause no advance or delay therebetween in the rotational angle. A typical constant velocity joint is illustrated in FIGS. 12A and 12B. In these drawings, an outer race 1 of the constant velocity joint has a recess 2 for housing balls, cages, etc. The recess 2 is ironed so that the opening 2a has a smaller diameter than does the interior, that is, the interior surface of the race 1 defining the recess 2 curves into the recess in radially outward directions. The inner wall of the recess 2 is formed with six ball-retaining grooves 3, and adjacent thereto, six cage-retaining portions 4.
Attempts have been made to manufacture outer races by cold forging, which is good in stock utilization and effective in saving resources. In cold forging, half-finished parts whose recesses are not yet ironed are supplied to dies and go through the forging process to become final products.
A forging method and apparatus for manufacturing constant velocity joints are known. FIGS. 13A and 13B show a prior art die while FIG. 14 shows a workpiece supplied to a working part of a punch. The prior art die comprises a group of groove-cutting punches 10 of the same number with recesses or ball-retaining grooves in the outer race, the punches 10 being disposed around a punch guide 11, as shown in FIG. 14, and portions adjacent to the ball-retaining grooves serve to retain cages.
The working part in the end of the punch 10 is mounted movable on a pivot 12. Numerals 13, 14 and 15 respectively indicate an ironing die, an ironed workpiece, and a spring for pivotally moving the punch 10.
A group of spaced apart punches 10 are disposed around the punch guide 11, and each punch has a working part at its upper end in FIGS. 13A and 13B, for cutting the ball-retaining groove. The workpiece 14, which is preformed as a hollow structure, comes into contact with the working parts of the punches set by the punch guide 11 and is then ironed with the use of the die 13 so as to narrow the outside diameter. After completing the ironing process, the punches 10 are moved relative to the punch guide 11 to pivot working parts inward, whereupon the group of punches is pulled out of the ironed workpiece 14.
The prior art, in which the removal of the punches from the ironed workpiece is done after pivoting the working parts of the punches inward, necessitates providing spaces between respective punches set in place by the punch guide. Therefore, the ironed workpiece was formed with excess metal raised portions at such positions corresponding to the spaces. After ironing, these raised portions which correspond to the cage-retaining portions were required to be mechanically shaved off for finishing. Thus, the prior art method was inefficient in requiring an additional manufacturing step and material waste.
Further, the prior art method has the added disadvantageous of causing malfunctions of the machine in that, for example, the aforementioned raised portions can prevent the punches from being drawn radially inward for removal.
These disadvantages are caused by the requirement of providing spaces between the punches when they are set by the punch guide, but the provision of such spaces has been considered to be essential in order to draw the punches radially inward after the formed process.
A proposed improved method has been made in order to eliminate the latter mechanical process subsequent to the forming process. As shown in FIG. 15, a workpiece 16 was preformed with escape grooves 16c at positions corresponding to cage-retaining portions 16b adjacent to ball-retaining grooves 16a. An ironing process was performed with the escape grooves being respectively located at the spaces between the punches, so as to prevent the portions of the workpiece in the spaces between the punches from rising above the cage-retaining surfaces and to confine such rise to within the escape grooves. This method was proposed to reduce the number of processes of manufacture by eliminating the mechanical finishing process.
When performing the above proposed method, however, it has been difficult to fix the width, length and depth of the escape groove to its dimensions so as to serve to eliminate the mechanical process subsequent to the forming process, because a change in quantity of the raised portion is caused by a very small change in the volume of the workpiece. If the product may be left with groove traces where the escape grooves had been performed, then it may be grooved to the extent that will avoid the raised portions. But if the existence of such groove traces is unacceptable, it is still necessary to mechanically shave off the traces in the cage-retaining portions after the forming process. Considering that this method may still be disadvantageous in terms of the number of processes required and stock utilization, this method does not in fact provide an improvement over the prior art.